A refrigeration system typically consists of four major components connected together via a conduit (preferably copper tubing) to form a closed loop system. The four major components are a compressor, a condenser, expansion device and an evaporator. A refrigerant circulates through the four major components and will have its pressure either increased or decreased and its temperature increased or decreased.
The refrigerant is continuously cycled through the refrigeration system. The main steps in the refrigeration cycle are compression of the refrigerant by the compressor, heat rejection of the refrigerant in the condenser, throttling of the refrigerant in the expansion device, and heat absorption of the refrigerant in the evaporator. This process is sometimes referred to as a vapor-compression refrigeration cycle.
The vapor-compression refrigeration cycle is used in air conditioning systems, which cool and dehumidify air in a living space, in a moving vehicle (e.g., automobile, airplane, train, etc.), refrigerators and heat pumps.
In an ideal refrigeration cycle, the refrigerant enters the compressor as saturated vapor and is compressed to a very high pressure. The temperature of the refrigerant increases during this compression step. The refrigerant leaves the compressor as superheated vapor and enters the condenser. A typical condenser comprises a single conduit formed into a serpentine-like shape so that a plurality of rows of conduit is formed parallel to each other. Metal fins or other aids are usually attached to the serpentine conduit in order to increase the transfer of heat between the refrigerant passing through the condenser and the ambient air. As heat is rejected from the superheated vapor as it passes through the condenser, the refrigerant exits the condenser as saturated liquid.
The expansion device reduces the pressure of the saturated liquid thereby turning it into saturated liquid-vapor mixture, which is throttled to the evaporator. The temperature of the refrigerant drops below the temperature of the ambient air as it goes through the expansion device. The refrigerant enters the evaporator as a low quality saturated mixture comprised of approximately 20% vapor and 80% liquid. Note that the quality is defined as the mass fraction of vapor in the liquid-vapor mixture.
The evaporator physically resembles the serpentine-shaped conduit of the condenser. The refrigerant completely evaporates by absorbing heat from the refrigerated space and leaves the evaporator as saturated vapor at the suction pressure of the compressor and reenters the compressor thereby completing the cycle.
The efficiency of a refrigeration cycle is traditionally described by an energy-efficiency ratio (EER). It is defined as the ratio of the heat absorption from an evaporator to the work done by a compressor. ##EQU1##